How do sleep and stress affect weight?

Short sleep and chronic stress don't directly "make you fat," but they do affect appetite, cravings and food choices: after a short night you're usually hungrier, crave more sweet and fatty food, and have less energy to move. Long-lasting stress can also increase emotional eating and make meals more irregular. That's why enough sleep (at least 7 hours for adults) and stress management are a real part of any weight-loss plan, not a side note.

This article is for education. It doesn't replace a visit with your own doctor or their advice.

Short sleep and appetite: what happens?

Hunger and fullness hormones

Two well-known hormones play a role in regulating appetite: ghrelin, which signals hunger, and leptin, which carries part of the message of fullness and stored energy. In some lab studies, limiting sleep for a few nights raised ghrelin, lowered leptin and increased the feeling of hunger.

Of course, the picture isn't that simple. Not every study has shown these hormone changes in the same way, and people's bodies differ. But one finding is fairly consistent: people usually eat more after short sleep, especially late-night snacks and high-calorie foods.

A tired brain, harder decisions

Short sleep isn't only about hormones. When you're tired, the parts of the brain responsible for planning and self-control work less well, and the brain leans toward immediate reward. That's why at eleven at night, after a long day, biscuits, nuts and sunflower seeds (tokhmeh) look far more tempting than a glass of yogurt.

Staying awake means more time to eat

There is also a simple reason: the later you go to bed, the more waking hours you have in which to eat. Late-night gatherings, watching a series until midnight with tea and sweets alongside, all add calories you hadn't counted in your day.

Less energy to move

After a bad night, walking and exercise are the first things to go. Short sleep can also temporarily lower the body's sensitivity to insulin. In short, poor sleep makes the "eating" side heavier and the "burning" side lighter.

Stress and cortisol: what do we actually know?

You've probably heard that "cortisol makes you fat." That statement is half true, and it's worth looking at more carefully.

Cortisol is a hormone the body makes in response to stress, and it is essential for life. In conditions where the body makes abnormally large amounts of cortisol, or with long-term use of corticosteroid medicines, weight gain and belly fat are seen. But with the ordinary stresses of life, the relationship between cortisol and weight is complicated and varies from person to person, and you can't say that every stress adds weight directly through cortisol.

What is clearer is the effect of stress on behavior:

• Some people eat more under stress and reach for sweet and fatty foods
• Some skip meals and then overeat at night when they are very hungry
• Stress usually spoils sleep too, which starts a cycle of short sleep and cravings
• There is less time and energy for cooking and movement

If you notice you turn to food when you are stressed or upset, you are not alone. We say more about it in Emotional eating.

Sleep and stress are not the "hidden magic" behind weight gain, but they shift your hunger, cravings and energy. When you get them in order, sticking to your diet becomes much easier.

How much sleep is enough?

In their joint statement, the American Academy of Sleep Medicine (AASM) and the Sleep Research Society (SRS) recommend that adults regularly sleep at least 7 hours a night. It isn't only the number of hours; a regular bedtime and wake-up time and the quality of your sleep matter too.

Habits that spoil sleep, and a simple swap

Common habit	Why it's a problem	Suggested swap
A heavy dinner at 10 or 11 pm	A full stomach and heartburn make sleep lighter	A lighter dinner about two to three hours before bed
Strong tea or coffee after the afternoon	Caffeine stays in the body for hours	After the afternoon, weak tea, a caffeine-free herbal tea or water
Phone in bed	Exciting content and screen light keep the brain awake	Phone outside the room, or at least put away for the last half hour
A different bedtime on weekends	The body clock gets thrown off	A roughly fixed wake-up time, even on Fridays
A long late-afternoon nap	You can't fall asleep at night	A short nap of about 20 minutes, taken before late afternoon

Sleep hygiene for an Iranian lifestyle

Sleep advice is usually written for a life where dinner is at seven. But in many of our homes, dinner is ready at ten and guests stay until midnight. So let's make it realistic.

Late dinners

If you can't change the family's dinner time, change the size of it:

1. Have a proper late-afternoon snack, like yogurt with cucumber or bread with cheese and walnuts, so you're not starving by ten.
2. Serve a lighter dinner: one serving spoon (kafgir) of rice instead of two, with more salad, or lentil soup and yogurt instead of a greasy stew.
3. If you stay up after dinner, ten minutes of walking or tidying the kitchen is better than lying in front of the TV.

Evening tea and caffeine

Tea is part of our culture, but strong tea at night, especially with sugar or sweets, brings both caffeine and sugar. You don't have to give it up:

• Make tea after sunset weaker, or switch to herbal teas like dried lime (beh-limoo) or chamomile
• Move coffee, caffeinated soda and energy drinks to before noon or early afternoon
• Cut back the sugar with your tea little by little; for example from two cubes to one

Phones and screens

Scrolling in bed is one of the biggest thieves of sleep. It takes an hour of it without you noticing.

• Set a "quiet hour" for your phone and take its charger out of the bedroom
• If you use your phone as an alarm, keep it away from the bed
• Instead of scrolling, read a few pages of a paper book or do a few minutes of slow breathing

A few more simple rules

• A fixed wake-up time matters more than a fixed bedtime; start with that
• Keep the room dark, cool and quiet
• Get a little natural light in the morning; a few minutes by a window or outside
• If you've been awake in bed for more than about twenty minutes, get up and do something calm until you feel sleepy

Simple tools to lower stress

You can't remove stress, but you can change how you respond to it.

Walking

Walking improves mood, improves sleep and helps with weight control. The World Health Organization recommends that adults get at least 150 minutes of moderate activity a week. Even a twenty-minute walk in the evening or after dinner is a good start. We wrote more ideas in Walking and sleep.

Slow breathing

When you're under pressure, a few minutes of slow breathing can help. A simple method:

1. Sit comfortably and put one hand on your belly.
2. Breathe in slowly through your nose until your belly rises, for about a count of four.
3. Breathe out more slowly through your mouth, for about a count of six.
4. Repeat five to ten times.

Social support

Talking with a friend, a walk with your sister or mother, or even a short phone call can lighten the load of stress. Isolation usually increases both stress and emotional eating.

Small habits instead of big decisions

When you're tired and stressed, big plans get dropped quickly. Choose one small habit, such as "the phone goes away at eleven" or "I walk for ten minutes after dinner," and focus on just that for a few weeks. In The psychology of habit we explain why small steps last longer.

When should you see a doctor?

Some sleep problems don't go away with a change of habits and need a medical check:

• Ongoing insomnia: if for several weeks most nights you have trouble falling asleep, wake in the middle of the night, or wake very early and can't get back to sleep
• Loud snoring, pauses in breathing during sleep that people around you have noticed, or waking with a feeling of choking; these can be signs of obstructive sleep apnea, which is linked to extra weight and can be treated
• Severe daytime sleepiness despite enough sleep, especially if you nod off at the wheel
• Stress, anxiety or low mood that has lasted several weeks and has affected your work, your family or your eating
• Repeated episodes of binge eating that feel out of control; this can be a sign of an eating disorder, and there is specialist help for it

Don't take sleeping pills or supplements without your doctor's advice either.

Summary

Short sleep and chronic stress don't directly build fat, but they raise hunger, strengthen cravings and lower the energy to move. At least 7 hours of regular sleep, a lighter dinner, weaker tea at night, the phone outside the bedroom, a daily walk, slow breathing and talking with people close to you are simple but effective tools. If you have serious insomnia or snoring, be sure to talk to your doctor.

If you'd like your sleep and habits to be considered in your meal plan too, at Rejimist a doctor writes your personal diet from your questionnaire and stays with you through a short daily check-in by text message. Begin at start your diet.

Sources

• Watson NF, et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep, 2015.
• Spiegel K, et al. Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Annals of Internal Medicine, 2004.
• Taheri S, et al. Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index. PLoS Medicine, 2004.
• Al Khatib HK, et al. The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis. European Journal of Clinical Nutrition, 2017.
• Adam TC, Epel ES. Stress, eating and the reward system. Physiology & Behavior, 2007.
• World Health Organization (WHO). Guidelines on Physical Activity and Sedentary Behaviour, 2020.